The Diagnosis of Food Allergies
The diagnosis of food allergies can seem complicated because reactions to foods are often delayed and may be affected by many factors, including insufficient rest, stress, and other allergens we are exposed to at the same time. Indeed, it is usually impossible to determine what you are allergic to on your own if you have more than a very few food allergies. Therefore, medical testing and help from the right health professionals is important. Click here for URLs of medical associations such as the American Academy of Environmental Medicine where you can find someone who can help you in your area.
Elimination and challenge was the first type of testing used for food allergies. It is still often used in the clinical ecology units of hospitals or clinics and is considered the “gold standard” method of allergy testing for foods. The patient either fasts for several days (in a clinic under medical supervision) or at home eliminates the foods to be tested from the diet for five to ten days. The suspected foods are then eaten one at a time and symptoms are recorded. This method is difficult to use for delayed (non-IgE) food allergies. In severely allergic patients, it can be dangerous and should be used only under medical supervision, such as in a clinic setting.{1}
Intradermal or scratch skin tests are used by many conventional allergists and are good for inhalant allergies. However, they are usually not reliable for food allergies because they detect only IgE-mediated food allergies, which make up only about five percent of all food reactions.{2}
Provocation-neutralization testing is the most common in-office, or in-vivo test for food allergies. A small amount of a dilute extract of the food to be tested is injected into the skin of the patient’s arm or given under the tongue. Any symptoms that result are recorded and the skin reaction is monitored. Then injections or sublingual drops of weaker or stronger dilutions of the same food extract are given. The dilution which does not provoke a skin reaction and clears up the patient’s symptoms is the “neutralizing dose” and is used for neutralization treatment. (See page 10 of The Ultimate Food Allergy Cookbook and Survival Guide for more information about neutralization). This test works best with food reactions that happen quickly whether mediated by IgE or IgG3. It is about 80% accurate.{4}
Some doctors consider only in vivo tests (such as elimination-and-challenge or provocation-neutralization) definitive for food allergies because they have been tested in double blind studies. However, although our allergist uses the provocation-neutralization method for all food allergy testing for adults, when my son needed allergy testing at age four, the doctor used a blood test to spare such a young child the trauma of multiple needle sticks. We were instructed to re-test all the foods that showed up as possible problems for my son by doing elimination and challenge tests at home. In this time of economic struggle and medical insurance which covers less and less every year (if you are fortunate enough to have it), some patients chose to pay out-of-pocket for blood tests for food allergies rather than bear the cost in both time and money of allergy testing in a doctor’s office. There are several types of blood tests including RAST (Radio-Allergo-Sorbent Test), ELISA (Enzyme Linked Immuno-Sorbent Assay), and ELISA/ACT (Enzyme Linked Immuno-Sorbent Assay/Activated Cell Test). RAST and ELISA tests can detect either IgE or IgG antibodies to foods in the blood sample.{5} ELISA/ACT tests can detect IgG, IgA, and IgM antibodies, immune complexes, and cell activated reactions.{6} Thus, blood tests can detect the factors implicated in delayed as well as immediate food allergies, but to be definitive, food allergies that show up on a blood test should be confirmed by elimination and challenge.{7} If you elect to have a blood test, consult your doctor about the advisability and safety of confirming food allergies that show up as positive by an elimination and challenge test. Click here for URLs of laboratories that do blood tests for food allergies. These laboratories may also be able to direct you to a nearby allergy clinic.
Footnotes:
1. Reno, Liz, M.A. and Joanna Devrais, M.A. Allergy Free Eating, Celestial Arts, Berkeley, CA,1995, p.28.
2. Ibid, pp. 29-30.
3. Ibid, pp. 29-30.
4. Personal communication from W. A. Shrader, Jr., M.D., April, 1997.
5. Reno, Liz, M.A. et al, pp. 30-31.
6. Interview with Russell Jaffe, M.D., Ph.D., “Allergy Testing,” Mastering Food Allergies Newsletter, #44, April 1990, p. 3.
7. Personal communication from W. A. Shrader, Jr., M.D., April, 1997.
The information on this page is abridged from
The Ultimate Food Allergy Cookbook and Survival Guide ($24.95, eBook $13) © 2007
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